This invention relates to a process for dynamically separating a contaminating zone and a zone to be protected, communicating between each other through at least one separation zone, by means of a clean air curtain obtained by injecting at least two adjacent clean air jets into the separation zone in the same direction.
The process according to the invention may be used in many industrial sectors.
A first family of industries concerned by this process includes all industries (food processing, medical, biotechnologies, high technologies, etc.), in which it is necessary to prevent the atmosphere in a given working zone from being contaminated by the ambient air carrying thermal, microbial, and/or particular and/or gaseous contamination.
Another family of industries concerned by the process according to the invention includes industries (nuclear, chemical, medical, etc.) in which individuals and their environment must be protected from toxic or dangerous products placed inside a confinement containment.
At the present time, there are two types of solutions for dynamically separating two zones communicating with each other through one or more separation zones, for example in order to allow objects to be brought in and out, these two types being protection by ventilation and protection by an air curtain.
Protection by ventilation consists of artificially creating a pressure difference between the two zones so that the pressure in the zone to be protected is greater than the pressure inside the contaminating zone. Thus, if the zone to be protected contains a product that could be contaminated by ambient air, a laminar flow is injected into the zone to be protected that blows outwards through the separation zone. In the opposite case in which personnel and the environment outside a contaminated space need to be protected, dynamic confinement is achieved by using extraction ventilation in this contaminated space. In each case, an empirical rule imposes a minimum ventilated air speed of 0.5 m/s in the plane of the separation zone through which the two zones communicate in order to prevent contamination from being transferred into the zone to be protected.
However, the efficiency of this ventilation protection technique is not perfect, particularly in a so-called xe2x80x9cinfractionsxe2x80x9d situation, in other words when objects are transferred through the separation zone inserted between the two zones. Furthermore, this type of protection makes it necessary to process and control the entire zone to be protected from the contaminating external atmosphere or the entire contaminated zone. When the zone to be processed and controlled is large, this introduces a particularly high investment in operating cost. Finally, this technique of protection by ventilation only provides protection in one direction, in other words it is only useful when contamination transfers are only possible in one direction.
The air curtain protection technique consists of simultaneously injecting one or several adjacent clean air jets in the same direction into the separation zone between the two zones, which form an immaterial door between the zone to be protected and the contaminating zone.
Note that according to the theory of turbulent plane jets, a plane air jet is composed of two separate zones; a transition zone (or core zone) and a development zone.
The transition zone corresponds to the central part of the jet adjacent to the nozzle in which the speed vector is constant. This zone corresponds to the part of the jet in which there is no mix between the injected air and the air on each side of the jet. Considering a cross-section through a plane perpendicular to the plane of the separation zone, the width of the transition zone gradually decreases as the distance from the nozzle increases. This is why this transition zone is called a xe2x80x9ctonguexe2x80x9d throughout the rest of the text.
The development zone of the jet is the part of this jet located outside the transition zone. In this jet development zone, outside air is entrained by the jet flow. This results in variations in the speed vector and mixing of air. Air entrainment on both sides of the jet within this development zone is called xe2x80x9cinductionxe2x80x9d. Thus an air jet induces an air flow on each of its faces which depends particularly on the injection flow of the jet considered.
Document JP-B-36 7228 proposes producing an air curtain by simultaneously injecting three adjacent air jets in the separation zone and in the same direction. More precisely, a relatively fast air jet is injected between two relatively slow air jets. This arrangement is supposed to provide more efficient confinement than a single air jet, because the entrained air mixed by the central jet is only slightly contaminated, and originates from relatively slow jets injected on each side of this central air jet.
However, this document does not consider the length of the tongues of each jet, nor their injection flows, such that the confinement efficiency is very uncertain.
Document FR-A-2 530 163 proposes to control confinement in a polluted room with an opening by injecting an air curtain into it consisting of two clean adjacent air jets blowing in the same direction. More precisely, dynamic separation is provided by a first relatively slow jet (called the xe2x80x9cslow jetxe2x80x9d), for which the tongue entirely covers the opening. The second jet (called the xe2x80x9cfast jetxe2x80x9d) is faster than the slow jet, and is installed between the slow jet and the zone to be protected. Its function is to stabilize the slow jet by a suction effect which brings this slow jet into contact with the fast jet.
Document FR-A-2 530 163 describes that the slow jet tongue is sufficiently long to cover the entire opening when the width of the injection nozzle for this slow jet is equal to at least one sixth of the height of the opening to be protected. It also states that injection flows of the two air jets must be such that the air flow induced by the surface of the fast jet which is in contact with the slow jet is approximately equal to the injection flow through the slow jet.
Document FR-A-2 652 520 suggests using an air curtain to protect a clean working zone provided with an opening, from the contaminating external environment. The main characteristics of the air curtain are similar to the characteristics described in document FR-A-2 530 163. It is also specified that the injection speed of the slow jet must be of the order of 0.4 m/s or 0.5 m/s. It is also specified that jets should be emitted such that the external surface of the fast jet reaches the limit of the opening plane. Due to the jet expansion angles, this results in an angle of about 12xc2x0 between the median plane of the jets and the plane of the opening.
Document FR-A-2 652 520 also proposes simultaneously injecting clean ventilation air at a temperature adapted to requirements, inside the working zone to be protected. This document states that this clean ventilation air must be injected at a flow approximately equal to the flow induced by the surface of the fast jet that is in contact with clean ventilation air.
Furthermore, document FR-A-2 652 520 also indicates that the intake grille through which the two jets are recovered is located outside the opening and below the work station, so that the ventilation in the contaminated zone can be controlled. Furthermore, the two side walls which delimit the opening are extended towards the outside over a distance equal to at least the thickness of the air curtain.
Document FR-A-2 659 782 proposes adding a third relatively slow clean air jet to the two clean air jets described in document FR-A-2 530 163, so that the fast air jet is located between the two adjacent slow jets and in the same direction.
With this arrangement, which uses the main characteristics described in documents FR-A-2 530 163 and FR-A-2 652 520, the clean ventilation air injection flow inside the zone to be protected is considerably reduced. Furthermore, dynamic confinement is provided in both directions, which was not the case in the previous documents.
The reduction in the injection flow of clean ventilation air inside the zone to be protected is a result of the fact that induction in this zone is obtained as a result of the development zone of one of the slow jets, and no longer the development zone of the fast jet as was the case of an air curtain with two jets.
Despite the improvements made to the air curtain technique in these various documents, experiments and simulations made by the applicants have shown that the confinement efficiency obtained with air curtain devices described in documents FR-A-2 530 163, FR-A-2 652 520 and FR-A-2 659 782 could be considerably improved, particularly in infraction situations.
The purpose of the invention is a process for dynamic separation of two zones communicating with each other through at least one separation zone using an air curtain, the principle of which is similar to the principle described in documents FR-A-2 530 163, FR-A-2 652 520 and FR-A-2 659 782, but for which the confinement efficiency is significantly improved, particularly in infraction situations.
According to the invention, this result is achieved by means of a process for dynamic separation of a contaminating zone and a zone to be protected, communicating with each other through at least one separation zone, this process comprising the following steps:
a first relatively slow clean air jet is injected into the said separation zone at a first injection flow, comprising a tongue capable of covering the entire separation zone;
a second relatively fast clean air jet is injected at the same time into the separation zone, at a second injection flow, adjacent to and in the same direction as the first jet, between the zone to be protected and the first jet;
this process being characterized by the fact that the second injection flow is adjusted so that the air flow induced by the surface of the second jet in contact with the first jet is not greater than about half of the first injection flow.
The applicants have discovered and verified by experiments and by calculation, that all these characteristics are essential in order to obtain a xe2x80x9cbarrier effectxe2x80x9d between the two zones, in other words so that the tongue effectively covers the entire separation zone.
If the induction at the surface of the fast jet created by the jet blower flow is too high, it may be considered that the slow jet tongue is overconsumed with the consequence of reducing the length of the slow jet; consequently, the coverage of the opening to be protected is imperfect (which is the case of all documents according to prior art). On the other hand, if the fast jet flow is too low, stabilization of the slow jet by induction of the surface of the fast jet in contact with the slow jet is not maximized. This is why applicants have determined that it is essential that the air flow induced by the surface of the second (fast) jet in contact with the first (slow) jet is less than, or preferably approximately equal to half of the injection flow of this first jet, and not equal to the entire injection flow as described in documents FR-A-2 530 163, FR-A-89 12861 and FR-A-2 659 782.
The air curtain may provide dynamic confinement in either direction if a third relatively slow jet is added to the first two jets. In this case, a third relatively slow clean air jet is injected into the separation zone at a third injection flow adjacent to the second jet and in the same direction as the first and second jets, between the zone to be protected and the second jet. The third jet comprises a tongue capable of covering the entire separation zone. The third injection flow is then adjusted so that it is approximately equal to the first injection flow, so that the air flows induced by the surfaces of the second jet in contact with the first and third jets respectively are not more than approximately half of the first and third injection flows. Due to these characteristics, the third jet effectively covers the entire separation zone.
Preferably, clean ventilation air is injected simultaneously inside the zone to be protected at an injection flow equal to at least the air flow induced by the second or third jet (depending on whether the air curtain has two or three jets), on the surface of the jet in contact with clean ventilation air. The applicants have discovered that this characteristic can give a xe2x80x9cpurifying effectxe2x80x9d in the zone to be protected, particularly in infraction situations through the air curtain.
In order to optimize the purifying effect, and regardless of the number of jets used to form the air curtain, it is advantageous to inject clean ventilation air at a speed such that the speed of this clean ventilation air divided by the plane area of the separation zone is equal to at least 0.1 m/s.
If internal ventilation is used, clean ventilation air is injected over the entire rear wall or top of the zone to be protected, towards the separation zone. Therefore, the wall through which the clean ventilation air is injected is parallel to or approximately perpendicular to the plane of the separation zone.
If it is also required to control the temperature inside the protected zone, clean ventilation air is injected at a regulated temperature.
In order to further optimize the barrier effect provided by the air curtain, all clean air jets are preferably injected in directions approximately parallel to the plane of the separation zone. Furthermore, all clean air jets are advantageously recovered by an intake located facing the injection nozzles of these jets in a plane approximately perpendicular to the direction of the clean air jets.
The barrier effect provided by the air curtain may also be optimized by extending the side walls of the openings, located on each side of the clean air jets, so that they extend towards the contaminating zone over a distance equal to at least the maximum thickness of the jets.